Time-lapse imaging (tSPI) is used to examine biological activity over natural cycles, like tides and daylight or anthropogenic variables like feeding loads in aquaculture.
A- slack winch-wire; B- oil-filled cylinder; C- piston rod; D- piston containing a small diameter hole; E- battery housing with magnetic reed switch, F- lead weights, G- camera (oriented vertically); H- light; I- Plexiglas guillotine filled with distilled water; J- sediment-water interface; K- 45° angle mirror reflecting the sediment-water interface profile 90° to the camera lens.
When calibrated using traditional grab samples or cores coupled with a few SP images, resolution allows identification of some infauna including the tubicolous sabellid polychaetes, a bisected nereid, and the mound produced by a sea cucumber seen in Figure 2.
When properly considered in conjunction with local geology and bioturbation levels, the depth and character of the ARPD can provide profound insights into the interactions between sediment geochemistry and biologic activity.
Graf's review (1992) supports the early observations of Jorgensen & Fenchel (1970) that sediments can be divided into oxic, suboxic, and anoxic levels with fundamental consequences for biota.
Some heavy metals, like cadmium and copper, are stabilised as sulphides and do not readily dissolve, but can be remobilised quickly and pollute boundary layer water if oxic conditions are restored (Graf 1992).
Rhoads and Germano (1982) developed a list of parameters taken from SPI in an effort to reduce and quantify specific environmental attributes and make them amenable to traditional statistical analysis.
For example, one of the reported effects of sustained aquaculture activity on coastal environments is the deposition and accumulation of organic-rich sediments near the production site whether from the faeces and pseudofaeces of shellfish or uneaten food and excretion of fin fish.
SPI allows much greater spatial coverage for a given amount of field time at the cost of the detailed sediment descriptors typically produced from physical cores (half phi interval texture analysis, carbon content, etc.).
SPI therefore offers the capability to examine dredge spoil mound morphology, compaction, winnowing, integration with native sediments, and, potentially, biological activity at a scale relevant to the macrofaunal assemblages under study.
With little information on bottom type, a simple, one-off, spatial impact study like that shown in Figure 5 with eight sites along an isobath, taking three replicate grabs from each, is fairly common and moderately powerful.
Prior data gathering including bathymetric, diver, towed-camera, ROV, or side-scan sonar observations would probably alter site placement and greatly enhance overall information and value.
Collecting a large number of point data from an SPI device is easily done where the resulting snapshots of the benthic character are automatically placed on a map of the study area in real time.
Other studies include those by Germano (1992) who investigated dredge-spoil disposal in Auckland's Hauraki Gulf, and Heip (1992) who summarised the value of SPI alongside meio- and macrofaunal sampling near an ocean drilling platform off the German Bight.
NOAA (2003 and references therein) report the widespread use of SPI for habitat mapping, dredge material cap monitoring, and oxygen stress (Nilsson and Rosenberg 1997) in estuarine, coastal, and deep water environments.
In order to form and test fundamental community ecology hypotheses or address applications such as impact assessment, conservation, and exploitation of the marine environment, one needs to investigate the complex interactions between sediments, organisms, and water.
Short-sequence DNA methods (e.g. Biodiversity Institute of Ontario 2006) are rapidly moving toward automated identification and diversity assessment techniques that hold the promise of revolutionising benthic ecology.
While remote sampling techniques often improve our point-sampling resolution, benthologists need to consider the real-world heterogeneity at small spatial scales and compare them to the noise inherent to most high-volume data collection methods (e.g. Rabouille et al. 2003 for microelectrode investigations of pore water).
New developments in the field of SPI will provide tools for investigating dynamic sediment processes, but also challenge our ability to accurately interpolate point-data collected at spatial densities approaching continuous data sets.
SP imagery as embodied in the commercial REMOTS system (Rhoads et al. 1997) is expensive (>NZ$60,000 at time of writing), requires heavy lifting gear (ca.
In such a dynamic environment, monitoring potentially transient disturbances like a spoil mound requires benthic mapping at fine spatial and temporal scales, an application ideally suited to SPI.
It is a conceptually simple matter to modify a consumer flatbed scanner so that its scan head (containing light source and sensor array) moves in a circular path instead of a plane as illustrated in Figure 7.
The optical assemblies of this type of scanner are fairly robust to vibration, but the traditional light source (a cold cathode tube of balanced colour temperature) is not.
A number of penetrating head geometries were explored using a series of ¼ scale models attached to a penetrometer and forced into sandy sediments under water.
Prior to deployment the device required a tether providing electrical and mechanical connections to the surface vessel and a frame to ensure that it entered the seabed perpendicularly.
The scanner technology chosen provided great depth of field (useful for identifying surface features), but required a large volume for the mirror assembly (which had to be strengthened to withstand vibrations).
Koenig et al. (2001) reviewed some exciting developments in optical sensors (also known as optodes or reactive foils) capable of resolving sub-centimetre oxygen distribution (using the non-consumptive ruthenium fluorescence method) and pH.
Biological and ecological theory is well enough advanced to be a full partner in environmental legislation, monitoring, and enforcement (Karr 1991) and can provide the appropriate local context for interpretation of physico-chemical results.
"A laboratory assessment of the survival and vertical movement of two epibenthic gastropod species, Hydrobia ulvae (Pennant) and Littorina littorea (Linnaeus), after burial in sediment."
Germano, J.D., Rhoads, D.C., Valente, R.M., Carey, D.A., Solan, M. (2011) "The Use of Sediment Profile Imaging (SPI) for Environmental Impact Assessments and Monitoring Studies: Lessons Learned from the Past Four Decades".